1. Field
One embodiment of the invention relates to an information storage apparatus, a method for correcting a feed pitch of a read/write head, and a method for forming a servo pattern. More specifically, the one embodiment of the present invention relates to an information storage apparatus configured to form a new servo pattern by using a servo pattern previously existing on a recording medium and execute recording and reproducing based on the new servo pattern, a method for correcting a feed pitch of a read/write head, and a method for forming a servo pattern by using the method for correcting the feed pitch of the read/write head.
2. Description of the Related Art
A servo pattern to be used for positioning control of a read/write head configured to execute data reading/writing for a storage medium is formed on the storage medium such as a magnetic disk to be mounted on an information storage apparatus such as a magnetic disk apparatus. The read/write head is positioned on a target track on the storage medium based on the reading result of the servo pattern.
The servo pattern to be formed on the storage medium is generally formed in a radial pattern from the inner circumference portion toward the outer circumference portion of the storage medium. Regarding other servo patterns, a servo pattern with a spiral shape and a servo pattern having a concentric servo pattern connecting to the servo pattern with the spiral shape is proposed (e.g., Jpn. Patent Appln. KOKAI Publication No. 61-59671).
The formation of the servo pattern on the storage medium is executed by an external servo track writer (STW). However, if the external servo track writer writes the servo pattern on the entire surface of the storage medium, since the writing of the servo pattern on the storage medium requires a long time, one external servo track writer is occupied for a long time period. Depending on the reason given above, since it is needed to increase the external servo track writer, there is the possibility of an increase in cost of an investment in facilities.
Conversely, in recent years, to reduce the cost of the investment in facilities for the external servo track writer, a method for magnetically writing the servo pattern within an information storage apparatus on which the storage medium is mounted is proposed (e.g., see U.S. Pat. No. 7,145,744 B1 and No. 5,668,679). In this method, the read/write head in the information recording apparatus forms the spiral servo pattern having the spiral shape, and forms the servo pattern in a radial pattern by using the spiral servo pattern.
Recently, various examinations related to practical realization of the method for forming the servo pattern with reference to the servo pattern having the spiral shape. This method forms, in advance, a first servo pattern including absolute position information at a portion of a storage medium, and also forms, in advance, a second servo pattern including relative position information on the entire surface of the storage medium, and forms a third servo pattern including the absolute position information on the entire surface of the storage medium by using the first and second servo patterns after mounting the storage medium in the magnetic storage apparatus.
However, various problems such as an accuracy problem and a cost problem have newly posed.
For instance, in a formation process (by an external STW) of the second servo pattern (spiral pattern), in a case where the feed speed in a radius direction of the head configured to form the second servo pattern is fast, its track pitch is made wide. In this case, even if the third pattern of the number of desired cylinders is tried to be written, there is the possibility that the read/write head reaches the outer circumference or the inner circumference of the recording medium before the third servo patterns of all the number of cylinders have been written. Conversely, in the formation process of the second servo pattern, in a case where the feed speed in the radius direction of the head is slow, its track pitch is made narrow. In this case, when the third servo patterns of the number of the desired cylinders have been written, there is the possibility that the servo pattern is not written in the outer circumference area or the inner circumference area of the recording medium and areas are left.
To cope with such a phenomenon, a method for estimating the gradient of a spiral servo pattern by using amplitude information of the spiral servo pattern to adjust a feed track pitch amount is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-140477. However, in the method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-140477, there is the possibility that it is impossible to eliminate the influence of variation of writing core width of the head to be used in formation of the spiral servo pattern, and influence of variation of reading core width of the head to be used in reading of the spiral servo pattern.